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- Question
In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time.
Options- A. True
- B. False
- Correct Answer
- False
ExplanationIn 180° mode three thyristors conduct simultaneously.
Power Electronics problems
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- 1. If ton and toff are the turn on and turn off times of a thyristor, then
Options- A. ton and toff are almost equal
- B. ton >> toff
- C. toff >> ton
- D. ton is about twice toff Discuss
Correct Answer: toff >> ton
Explanation:
Turn on time is less than 3 ?s while turn off time is between 10-300 ?s.- 2. In a full wave converter (M - 2 connection) feeding an RLE load, the peak thyristor current is 15 A. For fully controlled bridge circuit and same load current, the peak thyristor current will be
Options- A. 30 A
- B. 152 A
- C. 15 A
- D.
Discuss
Correct Answer: 15 A
Explanation:
In both the connections the output voltage and peak thyristor current are the same. Both are full wave rectifiers.- 3. A dc circuit breaker must use
Options- A. natural commutation
- B. forced commutation
- C. both natural and forced commutation
- D. either natural or forced commutation Discuss
Correct Answer: forced commutation
Explanation:
Natural commutation is possible only in ac circuits.- 4. The number of doped regions in a SCR is
Options- A. 2
- B. 3
- C. 4
- D. 5 Discuss
Correct Answer: 4
Explanation:
p = n = p = n.- 5. A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to
Options- A. one half wave of output
- B. one full wave of output
- C. two full waves of output
- D. either (b) or (c) Discuss
Correct Answer: one full wave of output
Explanation:
Since output frequency is 2f, one half wave of input must equal one full wave of output.- 6. Which of these commutation methods uses an auxiliary SCR?
Options- A. Class A
- B. Class B
- C. Class C
- D. Class D Discuss
Correct Answer: Class C
Explanation:
Class C commutation uses an auxiliary SCR and it is also called auxiliary commutation.- 7. In an SCR, the anode current is controlled by
Options- A. gate current only
- B. external circuit only
- C. both gate current and external circuit
- D. none of the above Discuss
Correct Answer: external circuit only
Explanation:
Once SCR has been triggered the gate has no control. Only external resistance controls the anode current.- 8. A single phase half wave controlled rectifier circuit has an R-L load. A freewheeling diode is also in the circuit. When freewheeling diode is conducting the SCR
Options- A. is forward biased
- B. is reverse biased
- C. may be forward biased or reverse biased
- D. forward biased initially but reverse biased afterwards Discuss
Correct Answer: is reverse biased
Explanation:
Free wheeling diode is forward biased only when SCR is reverse biased.- 9. A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a. During one cycle of input voltage, the total duration of conduction of freewheeling diode is
Options- A. a
- B. 2 a
- C. 4 a
- D. 0.5 a Discuss
Correct Answer: 2 a
Explanation:
Freewheeling diode conducts for a° in each half cycle.- 10. A DIAC has two terminals, anode and cathode.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
They are designated as T1 and T2 because diac can conduct in both directions.
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